1. Field of the Invention
This invention relates to a device for recording an image appearing on a cathode-ray tube on a sheet of a thermally developable photosensitive element always in a preferable density.
2. Description of the Prior Art
A thermally developable photosensitive element is a photosensitive element which is developed by heating at a temperature, for example, in excess of 100.degree.C after the image exposure has been effected by light. One such element is produced by Minnesota Mining and Mfg. Co., U.S.A. and is commercially available under the trade mark "DRY SILVER."
The density of the image on the thermally developable photosensitive element after development changes with the change in developing temperature to such an extent that even with a minor change in temperature of only about 1.degree.C the final print density is greatly affected. In an effort to obtain prints having a proper density, it is extremely difficult to design a thermal development station so that the developing device can always be maintained at a constant temperature. Generally, a thermostat is utilized to turn on or off the heater current, or the a.c. current for the heater is controlled by means of thyristors, etc., depending on the temperature so as to maintain the developing temperature constant. However, this tends to be affected by fluctuations in the voltage of the power supply or by ambient air conditions, and in addition, the developing temperature will change when a great number of prints are attempted to be obtained continuously. Furthermore, the thermal control response is late. If the thermal development is carried out by such a device as described, the print density varies, and thus prints of good quality are not obtained.